Not applicable.
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Not applicable.
The present invention relates to a hyper-eutectic Alxe2x80x94Si alloy having excellent abrasion resistance and free machinability. In the present invention, free machinability means that machinability is excellent.
The inventive hyper-eutectic Alxe2x80x94Si alloy can be applied to parts requiring abrasion resistance, such as swash plates of compressors for automotive air conditioners or cylinder blocks and cylinder liners of automotive engines.
Lubricants should be continuously fed to friction faces of swash plates of air conditioners in automobiles. Otherwise, seizure between friction metals occurs. So, metal materials having excellent abrasion resistance are suitable for use in such swash plates of compressors for automotive air conditioners.
On the other hand, in order to reduce the weight of automobiles, metals having low specific gravity are used. Also, even though metals are excellent in abrasion resistance and have low specific gravity, if they have poor workability including machinability, preparation cost becomes high. Metals, such as cast iron or bronze, have the advantage of excellent abrasion resistance and machinability but suffer from the disadvantage of high specific gravity. Therefore, in recent years, Al-based alloys have been widely used.
Typically, there is a representative hyper-eutectic Alxe2x80x94Si alloy having excellent abrasion resistance, lightweight property, and relatively superior workability, as shown in the following Table 1.
Such alloy is called A390 alloy in the related fields.
In alloys comprising two or more metals, the metals which are able to produce a congruent compound are used stoichiometrically, in which the congruent compound refers to that one metal of solid phase which is melted in the other metal of liquid phase at melted state or solid solution state. The alloy forming the congruent compound appears to be in equilibrium state.
The alloy which consists of compositions forming the congruent compound is called a eutectic alloy, in which the eutectic alloys exist at eutectic point in equilibrium diagrams of alloys. Alloys which are positioned at the left side of eutectic point in the equilibrium diagram are referred to as hypo-eutectic alloys, and alloys located at the right side of eutectic point in the diagram are called hyper-eutectic alloys.
As for Alxe2x80x94Si alloy, alloys having Si of 12.5 wt % correspond to congruent compounds. Commonly, if Si content ranges from 11 to 13 wt %, such alloy is called a eutectic alloy. On the other hand, hypo-eutectic alloys have Si content less than said range and hyper-eutectic alloys have Si content higher than said range.
In the case of applying to swash plates in compressors for automotive air conditioners, conventional A390 hyper-eutectic alloys representatively used in this field are subject to surface-treatment, such as anodizing or Sn plating, to improve abrasion resistance. Such conventional alloy is disadvantageous in that, unless lubricants are smoothly fed onto friction faces, seizure between the metals occurs. As well, cutting workability becomes poor and abrasion ratio of cutting tools is very high, thus increasing preparation cost.
There is thus a widely recognized need for materials having superior machinability and abrasion resistance to conventional A390 alloy.
It is an object of the present invention to provide a hyper-eutectic Alxe2x80x94Si alloy, which is excellent in free-machinability and abrasion resistance and maintains high strength through heat treatment.
The intensive and thorough research on a hyper-eutectic Alxe2x80x94Si alloy, carried out by the present inventors aiming to avoid the problems encountered in the prior arts, resulted in the finding that Alxe2x80x94Sixe2x80x94Cuxe2x80x94Bi alloy is formed under conditions of containing the minimized amounts of Mg and Ni, strongly reacting with Bi, whereby hyper-eutectic Alxe2x80x94Si alloys which have superior free-machinability, abrasion resistance and ductility to conventional hyper-eutectic Alxe2x80x94Si alloys, and maintain high strength through heat treatment, can be obtained.
As for conventional hyper-eutectic Alxe2x80x94Si alloys, there was no alloy containing Bi as a component.